Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.55   3.134%   $255.3082   $255.31   $255.30   $255.30  
  Purchase #2 $115.77   8.447%   $125.5491   $125.55   $125.55   $125.50  
  Purchase #3 $219.98   4.590%   $230.0771   $230.08   $230.10   $230.10  
  Purchase #4 $32.46   11.555%   $36.2108   $36.21   $36.20   $36.20  
  Purchase #5 $65.82   13.369%   $74.6195   $74.62   $74.60   $74.60  
  Purchase #6 $165.72   6.604%   $176.6641   $176.66   $176.65   $176.70  
  Purchase #7 $107.84   7.857%   $116.313   $116.31   $116.30   $116.30  
  7 purchase totals = $955.14       $1,014.7418   $1,014.74   $1,014.70   $1,014.70